Electrically-heated soldering tool



United States Patent O ELECTRICALLY-HEATED SOLDERING TOOL Louis L. Wolf, Minneapolis, Minn., assigne-r to Phillips Manufacturing Company, Inc., Minneapolis, Minn., 'a corporation of Minnesota Application July 19, 1951, Serial No. 237,519

9 Claims. (Cl. 2l926) My present invention relates to electrically-heated soldering tools and, more particularly, to an improved replaceable electrically-heated tip for soldering tools of the kind comprising a tubular metallic outer shell, which is enclosed at its outer end to provide a working surface and contains an electrical heating element in the form of a solid plug-like body of electrical insulating material, such as carbon or suitable carbon composition, contained within the bore of the outer shell and engaging the closed outer end thereof, adjacent the working surface. In soldering tips of this character, it has been customary to line the cylindrical portion of the bore of the tubular outer shell of the tip with a thermo-electrical insulating material and to insert into the lined bore of the outer casing a plug-like heating element of high temperature resistance material, such as carbon, having its outer end in thermo-electrical Contact with the closed outer end of the shell adjacent its working surface. In accordance with prior art practice, these plug-like resistance heating elements fit relatively loosely in the bore of the tip shell and were axially removable therefrom for replacement through the open inner end of the shell, and were maintained in thermo-electrical contact with the closed end of the shell by yielding pressure exerted from the inner end. It is general practice in soldering instruments of this kind to employ the metallic outer shell of the tip as one of the electrical circuit conductors for the heating element and to connect the other circuit conductor to the inner end of the plug-like heating element. In accordance with prior practice, the circuit conductor to the inner end of the heating element was an element completely independent of the heating element itself and was merely yieldingly pressed thereagainst for the purpose of achieving electrical coupling therebetween and the heating element and for the purpose of maintaining the heating element itself in thermo-electrical engagement with the closed outer end of the metallic' shell. Soldering instrument tips of this kind have been found objectionable by reason of the difficulty encountered in maintaining positive non-arcing contact between the plug-like heating element and the outer shell at one end and between the heating element and the internal conductor at the other end, the latter having been found the most serious source of annoyance. At the outset, these yieldingly maintained contact points provide quite satisfactory circuit connections, but due to the very high temperatures at these contact points (often sufficient to heat the outer shell to a cherry red temperature), oxidization sets in rapidly at these electrical contact points within the high temperature zone. This oxidization resulting from high temperatures and changing temperatures progressively builds up an electrical resistance at the contact points which causes progressively increasing degrees of arcing. This progressively increasing arcing at the contact points causes undesirably rapid deterioration of the heating element and conductors and ultimately results in failure of the heat-V ing element, requiring frequent cleaning of the areas or points of contact and frequent replacement of the pluglike heating element itself.

One of the important objectives of the instant invention is to provide an improved soldering instrument tip of the general character disclosed in which the useful life of the heating element is greatly increased.

Another important objective of the invention is to provide an improved soldering instrument tip of the general character disclosed which will operate for long ICC periods of time without service of the points of electrical contact to thev heating element.

A still further objective of the invention is the provision of an improved soldering instrument tip of the general character described wherein an electrical conductor of low. heat transfer capacity is positively united with the inner end of the heating element and extends rearwardly therefrom to a point remote therefrom and outside of the extreme high temperature zone at and immediately surrounding the heating element, and wherein a yielding contact is made with the rst-said conductor at a point sufficiently removed from the high temperature zone, that it will not be adversely affected by high ternperature or temperature changes. In accordance with the invention, this objective may be achieved in a tip structure wherein the heating element and the said positively united conductor are removable as a unit from the outer shell of the tip or may be achieved in a structure wherein the heating element is permanently applied inthe outer shell.

A still further object of the invention is the provision of an ,improved electrically-heated tip structure of the general character described wherein the solid plug-like heating element is snugly, positively, and permanently secured in the bore of the outer shell with its outer end in positive non-arcing engagement with the closed outer end of the shell, so that the heating element and shell are an integral unit to be installed and replaced as such. This positively eliminates deterioration, and service problems from arising at the point of contact between the plug-like heating element and the metallic outer shell. This improved structure further comprises an electrical conductor of low thermal conductivity, which positively unites with the inner end portion of the plug-like heating element, in a manner to form non-arcing contact therewith, and extends rearwardly therefrom to a point remote from the heating element and high temperature zone immediately surrounding the same, wherein contact may be made therewith by light pressure without danger of corrosion, oxidization or scaling or similar phenomena causing arcing at this point.

A still further objective of the invention is the provision of an improved method or process for producing the improved soldering instrument tips of the invention.

The above and other highly important objectives and advantages of my invention will become apparent from the following detailed specification, appended claims and attached drawings.

Referring to the drawings wherein like characters indicate like parts throughout the several views:

Fig. 1 is a fragmentary view, with some parts broken away, of a soldering tool or instrument embodying the invention;

Fig. 2 is a greatly-enlarged view in axial section of the tubular shank and tip portions of the soldering instrument shown in Fig. l; and

Fig. 3 is a fragmentary view in side elevation illustrating a slightly modified embodiment of the invention.

In Fig. 1, a portion of the non-metallic body of a hand soldering tool or instrument embodying the invention and which, in practice, is provided with a hand grip portion (not shown) is indicated as an entirety by 1. This non-metallic body 1 is a hollow structure and mounts at its upper front portion an electric lamp bulb 2, which throws a beam of light in the direction of the work area, but which constitutes no part of the present invention. Also mounted in the front end portion of the non-metallic body 1 is a long tubular shank 3 having an externally screw-threaded inner end portion 4 in threaded engagement with corresponding internal threads in the body 1. The shank 3 is not only threaded in the thick front wall 5 of the body 1, but is positively locked in place therein by opposed clamping nuts 6 and 7. By reference to Fig. l, it will be seen that a circuit head 8 is connected to the tubular shank 3 by a contact washer 9 interposed between and clamped between the nut 7 and the end wall S of the body 1. Another circuit lead is indicated by 10. These circuits 8 and 10 are adapted to be connected to a suitable source of low voltage current, such as the secondary winding of a step-down transformer (not shown) but having its primary winding connected to a suitable source of supply, such as the usual 115 volt power line (not shown). For the purpose hereof, either A. C. or D. C. current of relatively low voltage, usually below 30 voltage and preferably about 6 volts, may be employed. The manner in which the circuit leads 8 and 10 are operatively coupled in the heating circuit will be later described.

The tubular shank 3 is reduced in diameter at its outer end where it is internally threaded at 11 to receive the external screw threads 12 on the inner end portion of the metallic tubular outer shell 13 of the removable electrically-heated tip 14. The outer end of the outer shell 13 of the tip 14 is closed and tapered at 1S to provide a working tip surface 16. The shell 13 of the tip 14 may be made of any metal having suitable thermo-electrical qualities and also capable of being wetted or tinned with solder, but is preferably of copper. By reference to Fig. 2, it will be seen that the axial bore of the outer shell 13 is lined with an insulating sleeve 17 of material having low heat and electrical conductivity. A ceramic tube, such as porcelain, is preferably used for this purpose, although other materials, such as mica, are suitable. In accordance with the preferred embodiment of the invention, this insulating tube 17 is permanently anchored in the tubular outer shell 13 by means of a suitable high temperature cement or the like and extends slightly beyond the open inner end of the bore of the shell 13. By reference to Fig. 2, it will be noted that the outer end of the axial bore of the shell 13, adjacent the working surface 16, is tapered or generally conical to conform to the contour of the said working surface 16, the said conical or tapered outer portion of the bore extending beyond the outer end of the insulating sleeve 17.

The pluglike heating element, indicated as an entirety by 18, is in the nature of a solid body of high temperature electrical resistance material, such as carbon, fit snugly in the outer end portion of the insulating tube or sleeve 17, with its outer end extending beyond the outer end of the sleeve 17 and in tight surface contact with the tapered closed outer end of the bore of the shell 13. An electrical conductor of low heat conductivity and in the nature of a small diameter wire 19 extends rearwardly from the heating element 18 and has its outer end firmly anchored or secured in the inner end portion of the heating element 18, so as to provide a positively non-arcing electrical connection between the said conductor 19 and the heating element, as at 20. For the purpose of maintaining low heat conductivity in the lead wire 19, the diameter thereof is relatively small and the length thereof is many times its diameter. In fact, the lead wire 19 extends rearwardly to the rear end portion of the insulating sleeve or tube 17 where it is received in and permanently secured to a plug-like contact head 21 in a manner to provide a positive non-arcing connection. This contact head 21 is quite far removed from and remote from the heating element 18 and the high temperature Zone immediately surrounding the same. The metallic contact head 21 is preferably permanently cemented or otherwise secured in the inner end of the insulating tube or sleeve 17.

In the preferred embodiment of the invention, the plug-like heating element 18 is formed of powdered carbon resistance material, which is poured in a powdered state into the bore of the tip after the insulating tube or sleeve has been cemented thereinto. The method of producing this preferred product is to first pour into the lined bore of the outer shell a suitable quantity of suitable resistance material, such as carbon or carbon composition, and which may be formed into a solid integral body by application of pressure or pressure and heat. After a suitable quantity of powdered material has thus been poured into the lined bore, the lead wire 19 is inserted into the body of powdered material to a suitable depth, following which the powdered material is subject to high pressure applied by a suitable ram or the like through the then-open inner end of the insulating sleeve 17, it being understood that this ram or the like, which is not shown, will have a suitable bore through its axis to receive the lead wire 19. Heat will usually be applied to the material during the pressing process, but the presence or absence of heat will depend entirely upon the nature and requirements of the material being used. It will be understood, however, that suicient pressure or heat and pressure will be applied to form the powdered material into a solid body, which will be in tight, permanent physical contact with the interior of the insulating sleeve 17 and the closed end 15 of the metallic outer shell 13 and the lead wire 19. In this manner, positive non-arcing electrical connections are made between the heating element 18, the lead wire 20 and the closed working end of the outer shell 13. Hence, in accordance with the preferred method, the outer shell 13, the insulating sleeve 17, the solid body of the plug-like heat ing element 18, the lead wire 19 and the contact head 21 become an integral unit.

In a modified embodiment of the invention, the pluglike heating element 18 is pre-formed and cemented or otherwise firmly and permanently mounted in the insulating tube 17. In this case, the lead wire 19 is also locked in the rear end portion of the heating element during the forming process. In this instance, contact head 21 will also be permanently secured in the insulating sleeve 17 and positively united to the lead wire 19 to provide a non-arcing connection therewith. In the case 0f this modification, however, the insulating sleeve 17 will not be cemented or permanently secured in the outer shell 13 of the tip 14, so that a heating unit comprising the element 18, the insulating sleeve 17, the lead wire 19 and the contact head 21 will be removable from the outer shell 13 as a unit. In this case, non-arcing engagement between the outer end of the heating element 18 and the closed end portion 15 of the shell 13 will be maintained by yielding pressure exerted from the rear through the medium of a rigid conductor rod 22 and compression spring 23.

In the case of both the preferred embodiment of the invention and the modification described above, the preferred manner of permanently uniting the lead wire 19 to the contact head 21 is to pass the lead wire 19 through an axial bore in the contact head 21 and then weld or braze the lead wire 19 to the contact head 21 from the outside, as indicated at 24 in Fig. 2.

The compression spring 23 seats in a suitable recess 25 in the body 1 (see Fig. l) and has its other end seated against a flange 26 fast on the inner end portion of the conductor rod 22. Here it will be'noted that the circuit lead Wire 10 is connected to the conductor rod 22 through the fixed ange 26 thereof. Also, it will be noted here by reference to Fig. 1 that the spring 23 yieldingly urges the rigid contact rod to move outwardly and into snug electrical engagement with the rear end of the contact head 21. In the case of the modified arrangement described wherein the sleeve 17 and` elements contained therein are removable, this yielding pressure of spring 23 acting through rod 22 serves also to maintain the outer end of the heating element 18 in tight engagement with the closed outer end of the tip shell 13. By reference to Figs. 1 and 2, it will be seen that the bore of the tubular shank 3 is lined with a thermo-electrical insulating sleeve 27, which keeps the rod 22 centered and thermally and electrically insulated from the tubular shank 3.

The preferred manner of removably anchoring the tip unit in the tank 3 is by screw threads, as shown at 11 and 12 of Fig. 2. However, other means may be ernployed for this purpose. One such other means is indicated in the modified arrangement of Fig. 3 wherein the inner end of the shell 13 is unthreaded and is locked in place within the shank 3 by means of a set screw 28.

My invention has been thoroughly tested and found to be completely satisfactory for the accomplishment of the objectives set forth; and while I have shown a commercial embodiment of my improved device it will be understood that the same is capable of modification without departure from the scope and spirit of the invention as defined in the claims.

What I claim is:

1. An electrically-heated tip for soldering tools comprising a tubular metallic outer shell having an open anchoring end and a closed working end, a thermo-electrical insulating sleeve snugly fitted within the bore of the shell as a lining and being open at both ends, an electrical heating element in the form of a solid plug-like body of electrical resistance material snugly fitting in the open end portion of the insulating sleeve adjacent the closed working end of the shell with its outer end in thermo-electrical contact with the closed working end of the shell and its inner end materially spaced from the other end of the insulating tube, an electrical contact mounted in the open end portion of the insulating tube adjacent the anchoring end of the shell and remote from the heating element, an elongated electrical conductor generally axially disposed in the insulating tube and extending between and uniting the heating element and contact element, said electrical conductor being of greatly reduced diameter with respect to that of the heating element and the bore of the insulating tube and being of a length many times its diameter.

2. The structure defined in claim 1 in which the pluglike heating element is fast in the insulating tube.

3. The structure defined in claim 1 in which the pluglike heating element is fast in the insulating tube, and in v'lhilh the insulating tube is secured fast in the outer s e 4. The structure defined in claim 1 in which the pluglike heating element is fast in the insulating tube, and in which the insulating tube is integrally bonded to the outer shell, the outer shell, insulating tube, plug-like heating element, electrical contact element and electrical conductor forming a unitary replaceable tip structure.

5. The structure dened in claim 1 in which the pluglike heating element is fast in the insulating tube, and in which the insulating tube is snugly but removably applied in the outer shell, the insulating tube, plug-like heating element, electrical contact element and electrical conductor being removable as a unit from the outer shell of the tip.

6. The structure defined in claim 1 in which one end of the electrical conductor is imbedded and anchored fast in the inner end portion of the plug-like heating element.

7. The structure defined in claim 1 wherein the pluglike heating element is anchored fast in the insulating tube, the electrical conductor is imbedded and anchored fast in the inner end of the plug-like heating element, and

the insulating tube is integrally bonded to the interior of the outer shell.

8. The structure defined in claim 1 wherein the electrical conductor is imbedded and anchored fast in the inner end portion of the plug-like heating element, the plug-like heating element is securely anchored in the insulating tube, and the insulating tube is displaceable from the outer shell of the tip through the inner end of the atter.

9. The structure defined in claim 1 in which the outer end of the insulating tube is inwardly spaced from the outer end of the bore of the outer shell, and in which the plug-like heating element lls that portion of the bore of the outer shell outwardly of the insulating sleeve, that portion of the bore of the outer shell outwardly of the insulating sleeve being generally conical.

References Cited in the file of this patent UNITED STATES PATENTS 287,380 Hughes Oct. 23, 1883 695,995 Bachmann et al Mar. 25, 1902 1,130,218 Trood Mar. 2, 1915 1,462,431 Wagner July 17, 1923 1,463,951 Groven Aug. 7, 1923 1,533,959 Wagner Apr. 14, 1925 2,063,642 Vanden Berg Dec. 8, 1936 2,091,839 Tangeman Aug. 31, 1937 2,430,666 Burger Nov. 11, 1947 FOREIGN PATENTS 208,590 Switzerland May 1, 1940 550.333 Great Britain Ian. 4. 1943 

